Apparatus for cracking mineral oil



Nova 10, 1931 A. E. FEW, JR, ET AL APPARATUS FOR CRACKING MINERAL OILFiled June 26, 192.9 2 Sheets-Sheet S 6 e y w M 1/ 3 5. R w W a m w m ri 2; A 5 N m% 79 M W kuk a #1 W .m% a wm mm MW 3% M m m xui R w L H amfi m Lssmm Nov. 10, 1931. A. E. PEW, JR, ET AL APPARATUS FOR CRACKINGMINERAL OIL Filed June 26, 1929 2 Sheets-Sheet 2 7 Arrnwmmas "WW 5 r w WPatented Nov. 10, 1931 UNITED [STATES PA ENT; OFFICE ARTHUR E. Hair;.13., or BRYN MAWR, AND HENRY TI-IGMAS, or RIDLEY PARK,- PENN- ACORPORATION OF NEW JERSEY YLVANIA, ASSIGNORS TO SUN on. ooMraNv, orPHILADELPHIA, PENNSYLVANIA,

APPARATUS FOR CRACKING MINERAL OIL Application filed June 26,

In an application filed August 18, 1928, Serial No. 300,441, ofwhichthisapplication is in part a continuatiomwe describe a process and apparatusfor cracking mineral Oll. The apparatus comprises a boiler, adapted togenerate mercury vapor, connected, by outflowing vapor lines and byback-flowlng condensate lines, with a plurality of tanks, each of whichcontains a coil through which flows the oil that is to be heated andcracked. The coils of the several heating units are arranged in series.In each heating unit, heat exchange with the oil effects condensation ofthe mercury vapor, the condensate returning to the boiler through theback-flow connection.

' The use of mercury vapor as a heating medium involves grave danger ofserious results due to any rupture of a coil while the oil, under highpressure, is flowing therethrough in heat exchange relation with thesurrounding mercury vapor. No such system can be said to be of anypractical value, or to possess commercial possibilities, unless adequatesafeguards are provided to prevent such results from accidents of thischaracter. The object of the invention is to provide an apparatuscontaining all the provisions and safeguards required to make theprocess safe as well as economical and eflicient.

In the drawings:

Fig. 1 is a diagram of the cracking units, their connections with themercury boiler, and the conduits for mercury flow and mixed oil andmercury flow as hereinafter described.

Fig. 2 is a View, in side elevation, partly broken away, of one of theheating units, whose construction forms the subject-matter of LettersPatent No. 1,7 94,200, issued to-us February 24, 1931. r

Fig. 3 is a detail View of one of the automatic non-return valves. I

The cracking apparatus, per se, comprises four tanks a, b, c, and d, ineach of which is a coil of pipe e. The oil tobe cracked flows throughthe coils of any three of the tanks in series. For example, the oil mayflow through line 1 and hence through the pipe coil in tank a, thencethrough pipe 5 and through the coil in tank 6, thence through 1929.Serial No. 373,703.

pipe 6 and through the coil in tank 0 (in which the cracking iscompleted), and thence through pipe 9 and line 10. The pipes lead-: ingto and from the heaters are so arranged that any one or the tanks may bebypassed by the oil stream. In the example given, the tank d isby-passed. By propervalve manlpulation, either of tanks a, b and 0 maybe bypassed. For example, it tank a is bypassed, the oil flows from line4 into pipe 5, thence through tanks band 0 as above described, andthence through pipe 7 tank d andpipe 8 to line 10.

The described arrangement of four tanks of which any three may be inoperation simultaneously permits the continuous operation of the plant.When it is desired to clean out the pipe sections of any coil 6, it isby-passed and the previously by-passed coil is placed in series with theother two coils. v 7' Mercury vapor from boiler e flows through line 80and thence, in parallel, through branch pipes 81 into the several tanksthat are 1n operation. Mercury vapor enters each tank at the top.Condensed mercury flows out from the bottom of each tank through pipes82 and 83 into a clean-out 84. This clean-out communication, top andbottom, with one of the balancing columns of mercury 85, the otherbalancing column communicating with a line 86 flowing into a clean-out87, which communicates top and bottom, with a stand pipe 88, the bottomof which connects, through pipe 89, with the hquidmercury space of theboiler.

By throttling more or less the valves 90 on the mercury vapor inflowpipes 81, the pressure of mercury vapor in any given tank may be reducedin varying degree below boiler pressure, thereby making it possible topredetermine the temperature of condensation in each tank independently.The difference between the pressures in the boiler and in a given tankwill be taken care of by a corrsponding difference in the levels ofmercury in the two columns 85. It will thus be understood that providinga boiler pressure suflicient to givea vapor temperature above themaximum temperature of condensation that may be desired in any of thetanks, any desired temperature of condensation may be established in anyof the tanks. Thus extraordinarily exact temperature control isachieved, which is of the utmost importance, as will be explainedhereinafter.

In order to limit the maximum boiler pressure, a pipe 91 from themercury vapor feed or supply line 80 extends through a condenser 92 to aclean-out 94. On pipe 91 is a loaded safety valve 93. The clean-out isconnected, top and bottom, with a mercury seal 95, which connects withthe mercury condensate return flow line 86.

u The described means for maintaining a constant boiler pressure and'forgovernmg the pressure in each tank is more particularly described inLetters Patent No. 1,714,811 and No. 1,714,812, issued to us May 28,1929. 7 I

In the application of which this is in part a continuation we have shownand described the flow of charging stock through heat exchangers to theline 4. We have also shown and described the flow of cracked stockthrough line 10 and the method and means for separating the gasolinetherefrom. These features of the complete cracking plant form no part ofthe present invention and are not herein shown and described. Forpurposes of illustration it may be assumed that the charging stockenters line 4 at a temperature of (say) 435 F., that it may be heatedgradually or quickly in the first coilor in successive coils to atemperature of 865 F., that this temperature, once attained, may bemaintained in the coils, or may be slowly raised or otherwise varied,until the cracked stock flows out through line 10. There is, of course,a drop in pressure during the flow of the oil through the heat exchanger(not shown) before it enters line 1 and a very considerable drop inpressure during the flow of oil through the cracking coils. Thus theinitially imposed pressure on the oil may be assumed, for purposes ofillustration, to be 1200 pounds to the square inch and that before theoil reaches the pressure relief valve (not shown) on line10 the pressuremay be reduced to 650 pounds per square inch. To heat the first heatingor cracking unit through the temperature range435865 F. and maintain itat the higher temperature during the remainder of its flow through thatunit would require a mercury temperature of 866 F. or thereabouts. Tomaintain the temperature of the oil at 865 F. during its flow throughthe other units would require a mercury temperature of about 875 F. Thepressure in pounds absolute of mercury vapor at 87 5F. is about 80.Accordingly the boiler may operate at 80 pounds pressure, or at asomewhat higher pressure if the temperature is to be raised above 865 F.during the flow of the oil through the coils.

serious and even disastrous results.

The above data are given merely to illustrate the great difference inpressures to which the mercury and the oil are subjected. It is obviousthat, without special safety contrivances, if a coil should be ruptured,conditions would be created thatwould produce The shell of the tankwould be subjected to a pressure far beyond that which it is intended toresist.

Even if the shell should be made capable (which is practicable) ofresisting the vastly increased pressure, the oil and oil vapors wouldflow toward and into the boiler through the mercury vapor and mercurycondensate lines and contaminate the whole mercury vapor system, which,including the boiler, would be subjected to an immensely increasedpressure, with disastrous results.

Our invention comprises means, in the event of tubefailure, to preventserious rise of pressure in the tank and, particularly, in any otherpartof the mercury vapor system, to prevent contamination of the mercuryvapor system with oil, to limit the amount of oil that will escape intothe tank, to segregate any mixture of oil and mercury that willnecessarily result from the escape of a limited amount of oil from theruptured coil and to separate and recover the mercury from the mixture,to shut off the fiow of oil into the broken coil, to prevent a back flowof oil from a coil ahead into the broken coil, and to in effect isolatethe unit in which the accident occurs from the remainder of both themercury system and the oil system and insure against any serious injuryeven to the isolated unit. -The contrivances which we have providedtoinsure these measures of safety are of necessity wholly, or largely,automatic, but these automatically operating devices are supplemented bymanuallyoperable valves which are operable at any time and which,therefore, are operable to supplement the action of the automaticdevices.

Before describing the safety devices in detail, there should be adescription of the preferred construction of a heating unit.

The tank containing a coil 6 comprises a shell having circular dishedend headsr and s, and has openings at the top communicating with themercury vapor inflow pipes 81, and a connection at the top with a pipe96 on which is a relief valve 97 to relieve internal pressures. The pipesections forming the coil are, at one end, welded to head 1' from eitherthe inside or outside and are connected one to another by headers orreturn bends g, which are removable for cleaning purposes. Inside thetank, near the other end, is welded a ring of steel 25, which has beenmachined. A circular box a, with flat heads, is inserted inside thesteel ring. The other ends of the pipe sections are welded to the insidehead of box u, and headers or return bends 4; connect adjacent pipesections and, like headers 9, are removable. Welded to the other head ofbox u is a pipe or neck w, which extends out through head 8 and iswelded thereto. At the outer end of neck to are two 'fianges m boltedtogether to make a tight connection. Installed in neck we is anexpansion .joint y of the well known accordion type.

Mercury vapor fills the space around the tubes composing the coil 6butcannot penetrate the box It is thus possible, without hazard, for aman to enter box u through neck w and remove the return bends 0; whenthe tank is not in operation. Mercury vapor, however, will penetrate,through the sliding fit between box a and ring t, the space between boxu: and end head .9. Such vapors condense and are withdrawn through pipe83. The main condensate flows out through line 82. i

In case any of the pipe sections of any coil 6 should break, provisionshould be made to prevent oil vapors from flowing to the boiler eitherthrough the mercury vapor line or through the mercury condensate line. Anumber of provisions are made to insure against this possibility.

As before stated, at the top of each mercury vapor tank is a pipe 96equipped w1th a safety valve 97 which is set for any desired pressure,say 125 pounds." The pipes 96 leading from the several tanks connectwlth a common pipe line 98, which extends through a cooler 99 into asteel tank 100; In case a tube breaks, safety valve 97 opens as soon asthe pressure rises to, 125 pounds and the mixture of oil vapors andmercury vapor are cooled in cooler 99 to a temperature of (say) 450 F.,the mercury and most of the oil being thus liquefied. The liquidmercury, oil and oil vapors then enter tank 100' Due to the differencein the specific gravities of mercury and oil, the mercury collects inthe conical bottom and may be drawn ofi.

The mercury seals 85, hereinbefore 1 described, are of sufficient depthto hold a pressure in excess of 125 pounds and therefore, in event oftube failure, would prevent oil from flowing to the mercury boilerthrough the mercury condensate return 86. Any liquid oil or oil vaporsthat would enter pipe 82 would be trapped in the clean-out 84, due

, to the mercury seal 85.

In the event of tube failure, oil vapors are prevented from flowing tothe mercury boiler, by way of the mercury vapor inflow pipe 81 andinflow line 80, by means of the lower valve 30 on pipe 81. This valve.is a nonreturn valve that closes in case thepressure in the tank exceedsthe pressure in line 80. As a double safeguard, the upper valve 90 maybe a remote control hand operated valve.

While the above provisions insure against the contamination of themercury system with oil in case of tube failure, provision is alsomadeto limit the amount of oil that would escape into the tank. To thisend valves are installed which automatically isolate any heating tank'in' which a tube breaks. The valves are arranged in pairs,'31, 32, 33,34, 35,36,37, 38 and 39. Of each pair of valves, one valve'is anautomatic valve and the other a hand operated valve with remote controlfor safety; the automatic valve being adapted to close when the pressuredrops below a fixed point. Valves 41, 42, 43, 44and 45 are operated inorder to. by-pass any unit Let it be assumed that the plant is operatingon units a, b and c and that a break occurs in unit a. This would resultin animmediate drop in pressure in line 4; and the two automatic valvesof the two pairs of valves-3l and '32 would immediately shut, preventingfurther. flow of oil into unit a. By suitable 7 connections from thesevalves to'the power shut-ofi on the high pressure pump (not shown), thispump would stop. The other two valves of the two pairs of valves 31 and32 would then be closed by hand. :To prevent oil from backing up intothe unit in which a break has occurred from the unit immediately inadvance, one of the valves of each pair of valves 33, 35,, 37 and 39 ismade a check valve, the other valves of these pairs being handoperatedremotecontrol valves for double safety. 7

It will thus be clear that in case of a break in any of the coils e, thecorresponding unit is shut off both at the oil inlet andthe oil outlet.On the assumption that units a, b and a are in operation, valves41 and42 are shut,

they being used only as by-pass valves. If,

as above assumed, a break" occurs in unit w. the check valve of pair 33closes, preventing oil from backing'up from unit b into the broken coilin unit a.

By reason of the described closing of the automatic valve ofthe twopairs-of valves 31 and 32 and of the closing of the check valve ofthe-pair of valves 33, the inflow of oil to all three units is shutofli'. i It will thus be understood thatif a break occurs in any of theunits, there is no automatic diversion of the oil to the other units.All the cracking units are rendered inoperative.

The plant can be restartedby putting in series with the other two unitsthat have been in operation, the unit which theretofore has not beeninoperative. Thus, on the assumption that a break has'occurred in unit aand that all the units are rendered inoperative as described, units b, cand dean be put into operation by closing the hand valve of the pair ofvalves 32 and the hand valve of the pair of valves 33 and opening thehand valve 41.

The automatic non-return valves hereinbefore mentioned may'have anysuitable construction. One practicable construction is shown in Fig. 3.The stem of the automatic non-return valve 31 is secured to a diaphragm20, which, through a pipe 22, is subjected to the pressure on thedown-stream side of line 4.; this pressure holding the valve openagainst the action of a spring 21 coiled about the valve stem. Shouldthe pressure on the down-stream sidefall below the pressure on theupstream side the spring closes the valve. As soon as the valve shuts,the pressure on the up -stream side rises but cannot pass through thevalve.

What we claim and desire to protect by Letters Patent is:

1. An apparatus for cracking oil'comprising a tank provided with aninlet for a vaporous heating medium adapted to condense therein underrelatively low pressure, a-pipe coil extending through thetankfor'conveyance of the oil to be heated while subjected to relativelyhigh pressure, an outlet-from said tank and a safety valve on saidoutlet set to open, in the event of breakage of the coil, at a pressurebetween the pressures specified, a pipe connection for carrylng away themixture of heating medium and oil that escapes through said valve, andmeans interposed in the pipe connection for coolmgthe escaped mixtureand condensing the vapor ous heating medium, and means beyond the coolerfor separating the condensed heating medium by gravity. 2. An apparatusfor cracking oil comprising a tank provided with an inlet for a vaporousheating medium adapted to condense therein under relatively lowpressure, a pipe coil extending through the tank for conveyance of theoil to be heated while subjected to relatively high pressure, a sourceof supply of heating medium, a pipe connection r'rom said source ofsupply to said inlet and a nonreturn valve in said pipe connect-ionadapt-ed, 1n the event of coil breakage and consequent rise of pressurein the tank and escape of oil thereinto, to close said valve and therebyprevent backflow of oil through said pipe connection to the source ofsupply of heating medium.

3; An apparatus for cracking oil comprising a tank provided with aninlet for a vaporous heating medium adapted to condense therein underrelatively low pressure and with an outlet for condensate, a source ofsupply of heating medium communicating with said inlet and outlet, apipe coil eXtending through the tank for conveyance of oil to be heatedwhile subjected to relatively high pressure, and means to prevent escapeof oil through said inlet and outlet to the source of supply uponbreakage of the coil and consequent escape of oil into the tank and riseof pressure therein. 4. An apparatus for cracking oil comprising a tankprovided with an inlet for a vaporous heating medium adapted to condensetherein under relatively lowpressure, a pipe coil extending through thetank for conveyance of the oil to be heated while subjected torelatively high pressure, an outlet from said tank, a safety valve onsaid outlet set to open at a pressure between the pressures specified, asource of supply of heating medium communicating with said inlet, andmeans, operative in the event of coil breakage and a consequent rise ofpressure in the tank and escape of oil thereinto, to prevent back flowof oi-lthrough said inlet to said source of supply of heating medium.

5Q An apparatus for cracking oil comprising atank provided with an inletfor a vaporous heating medium adapted to condense thereinunderrelatively low pressure and with an outlet for condensate, a source ofsupply of heating medium communicating with said inlet and outlet, apipe coil extending through the tank for conveyance of oil to be heatedwhile subjected to relatively high pressure, and means to prevent escapeoi oil through said inlet and outlet to the source of supply uponbreakage oi the coil and consequent escape of oil into the tank and riseof pressure therein, said means comprising a non-return valve in saidinlet connection and a liquid seal in said outlet connection.

6. .An apparatus for cracking oil comprising a tank providedwith aninlet for a vaporous heating medium adapted to condense therein underrelatively low pressure, with an outlet for condensate and with anotherand normally closed outlet, a pipe coil extending through the tank forconveyance of the oil to. be heated while subjected to relatively highpressure, a source of supply of heating medium communicating with saidinlet and the first outlet and safety devices adapted to operate in theevent of breakage of the coil and consequent rise of pressure in thetank; said safety devices comprising means to prevent fiow of oilthrough said inlet and outlet to the source of supply and means to opensaid normally closed outlet.

7. An apparatus for cracking oil comprising a tank provided with aninlet for a vaporous heating medium adapted to condense therein underrelatively low pressure, with an outlet for condensate and with'anotherand normally closed outlet, a pipe coil extending through the tank forconveyance of the oil to be heated while subjected to relatively highpressure, a source of supply of heating medium communicating with saidinlet and the first outlet and safety devices adapted to operate intheevent of breakage of the coil and consequent rise of pressure in thetank;

.said safety devices comprising a liquid seal in the outlet connectionto said source adapted to hold a predetermined pressure substantially inexcess of the normal pressure in the tank, and a safety valvecontrolling the nor-- mally closed outlet and adapted to open under apressure substantially in excess of the normal pressure in the tank butbelow the pressure which said liquid seal is adapted to hold.

8. An apparatus for cracking oil comprising a tank provided with aninlet for a vaporous heating medium adapted to condense therein underrelatively low pressure, with an outlet for condensate and with anotherand normally closed outlet, a pipe coil extending through the tank forconveyance of the oil to be heated while subjected to relatively highpressure, a source of supply of heating medium communicating with saidinlet and the first outlet, and safety devices adapted to operate in theevent of breakage of the coil and consequent rise of pressure in thetank; said safety devices comprising a non-return valve in the inletconnection to said source, a liquid seal in the outlet connection tosaid source adapted to hold a predetermined pressure, and a safety valveadapted to allow the escape of mixed oil vapor and heating mediumthrough said normally closed outlet, said safety valve adapted to openunder a pressure substantially exceeding the normal pressure in the tankbut below the pressure which said liquid seal is adapted to hold.

9. An apparatus for cracking oil comprising a plurality of tanks adaptedto receive and condense a. heating medium under a relatively lowpressure, coils, arranged inseries, in the respective tanks, forconveyance of the oil to be heated under a relatively high pressure, anda valve on the connection between ad acent coils adapted, upon breakageof the first of two acent coils and the consequent reduction in pressuretherein, to close and thereby prevent the oil in the coil immediatelyahead of the broken coil from backing into the broken coil, and means tomaintain flow of oil through the coil ahead of the broken coil whileflow of oil to the latter is shut off.

10. An apparatus for cracking oil comprising a plurality of tanksadapted to receive and condense a heating medium under relatively lowpressure, coils, arranged in series, in the respective tanks, for conveyance of the oil to be heated under a relatively high pressure, an oilsupply pipe leading to the first coil of the series, a valve on saidsupply pipe, and a valve on the conncction bet-ween each two adjacentcoils, the valves ahead of and behind each coil being adapted to closewhen the pressure in said coil drops due to breakage of the coil,thereby isolating the broken coil and cutting off the flow of oilthereto, and means to maintain flow of oil through the remaining coilswhile the broken coil is so isolated.

11. An. apparatus for cracking oil comprising a tank provided with an.inlet for a vaporous heating medium adapted tocondense therein underrelatively low pressure,

with an outlet for condensate and with another and normallyclosedoutlet, a pipe coil extending through the tank for conveyance of the oilto be heated while subjected to rel atively high pressure, a source ofsupply of heating medium communicating with said inlet and the firstoutlet and safety devices adapted to operate in the event of breakage ofthe coil and consequent rise of pressure in the tank; said safetydevices comprising means to prevent flow of oilthrough said inlet andoutlet to the source of supply, means to open said normally closedoutlet, and melans to shut off flow of oil into the broken CO1 12. Anapparatus for cracking oil comprising a plurality of tanks adapted toreceive and condense a heating medium under a relatively low pressure,coils, arranged in series, in the respective tanks, for conveyance ofthe oil to be heated under a relatively high pressure, each tank havingan inlet for heat ing medium, an outlet for condensate and another andnormally closed outlet, a source of supply of heating mediumcommunicating with said inlet and the first named outlet, and safetydevices adapted to operate in the event of breakage of a coil andconsequent rise of pressure within the tank; said safety devicescomprising means to prevent flow of oil through said inlet and outlet tothe source of supply, means to open the normally closed outlet, andmeans to isolate the broken coil by shutting off inflow of oil to saidcoil and back flow of oil into said coil.

In testimony of which invention, we have hereunto set our hands, atPhiladelphia, Pennsylvania, on this 22nd day of June, 1929.

ARTHUR E. PEW, JR. HENRY THOMAS.

